1. Field of the Invention
The present invention relates to a wind tunnel structure, especially to a low speed wind tunnel having a set of adjustable boundaries.
2. Description of the Prior Art
Normally, vehicles such as cars, airplanes, and boats before manufactured are applied several times of wind tunnel tests for guaranteeing that the final products are power conservative, low wind resistant, and speed oriented. Therefore, the wind tunnel test result has always been a critical factor affecting the quality of the vehicles. Moreover, the precision of the wind tunnel test data compared to the real quality of the final product is absolutely requested. It has been a long term effort to decrease the difference between the wind tunnel test data and the real quality data of the product.
In a traditional wind tunnel test, a layer flow structure with a constant volume flow rate has been used for a long time. Referring to FIG. 1, the traditional wind tunnel 100 has a wind tunnel test section 101 constructed by a plurality of static boundaries 102. An object under test 103 is positioned in the center portion of the wind tunnel test section 101. In this traditional static boundary structure, when an air flow A is filtered by honeycomb and guided into the wind tunnel test section 101, a uniformly distributed flow field in the front section 104 will be formed in the wind tunnel test section 101. A boundary layer 105 will be formed against the inner wall of the static boundary 102 and it will turn to be thicker along the downstream, i.e., the flow outlet of the wind tunnel. For maintaining the constant volume flow rate of the air flow, the flow speed near the central axis of the wind tunnel has to increase. Therefore, in the traditional wind tunnel, the flow field is hard to maintain its uniformity, which in turn causes a considerable test error during the wind tunnel test.
Although a nested filter 106 may be used before the air flow A entering the wind tunnel test section 101 for regulating the air flow A to be a uniformly distributed air flow, it is still difficult to obtain one kind of uniformly distributed air flow for all kinds of different speeds because the single kind of cross-sectional area of the filter 106 can not meet different kinds of flow fields. Therefore, the effect of the filter 106 may be suitable for a specific speed of air flow not for other speeds of air flows. It is therefore to provide a new structure for solving the above problems.
The primary purpose of the present invention is to provide a new wind tunnel having at least one movable boundary for promoting the test precision in order to overcome the test error problems confronted in the traditional wind tunnel test.
Another purpose of the present invention is to provide a new nested filter for obtaining a more uniformly distributed flow field in the wind tunnel test section with simplified structure yet high precision of test result.
Further another purpose of the present invention is to provide a new adjustable boundary structure installed inside the wind tunnel test section for compensating back the cross section area occupied by the test object according to the shape of the object under test.
According to one aspect of the present invention, there is provided a low speed wind tunnel having at least one moving boundary. The wind tunnel comprises a wind tunnel test section constructed by a plurality of walls allowing an air flow to pass from an air inlet to an air outlet thereof. At least a movable wall is installed inside the wind tunnel test section. A driving device is provided for driving each movable wall to move based on the direction and speed of the air flow.